That number includes an unknown number of children and non-diplomat family members, but government officials are giving no further breakdown, citing privacy concerns.

Government officials, who briefed journalists on the condition of anonymity, say the ongoing problems are raising concerns about a new type of acquired brain injury, the cause of which remains a mystery. Officials say the cause could be human-made.

Spouses, children, or even parents of Canadian diplomats currently accompanying them in Havana will begin leaving the Cuban capital immediately.

Havana has now been declared an "unaccompanied post" in the Canadian foreign service -- a designation Cuba now shares with Afghanistan, Iraq, Libya and South Sudan.

Cuba is a favourite tourist destination for Canadians, with more than one million visiting the Caribbean island annually, but Global Affairs Canada says there is no evidence of any related ailments among Canadian travellers.

Canada is working with the United States -- many of whose personnel in Havana also took ill -- and Cuban authorities to try to solve the mystery.

Cuba says it is not responsible for the unexplained incidents, but the fallout has led the U.S. to recall many of its diplomats and expel Cuban representatives from Washington.

Global Affairs Canada said the new status of the Havana mission is the result of an environmental assessment of its staff housing completed in March that failed to turn up a cause. The decision is also being taken after the troubling findings of a University of Pennsylvania study of U.S. diplomatic staff.

"According to these specialists, medical information raised concerns for a new type of acquired brain injury. Additional research is needed to better understand this," said a statement Monday from Global Affairs Canada.

"The cause remains unknown, but could be human-made."

Government officials declined to give further details of the new medical findings and referred reporters to the study itself, which was published in February by the Journal of the American Medical Association.

Canada and Cuba continue to have "a positive and constructive relationship" and have been co-operating to find a cause since problems first surfaced about a year ago, the statement said.

But officials said Monday it remains a mystery that has no apparent precedent in diplomatic affairs.

About 27 people from 10 diplomatic families underwent testing when some complained of dizziness, headaches and difficulty in concentrating.

The symptoms developed amid concern about possible acoustic attacks in 2016 and 2017, but officials said Monday the theory of an acoustic or sonic attack has been ruled out.

Canadian diplomats in Havana were told Monday of the changes, and officials said they would be given time to evaluate any future career decisions, given the effect on their families.

Many of the embassy staff were due to rotate out and be replaced this coming August, but now all those involved will be given time to re-evaluate their next moves, officials said.

The Cuban embassy in Ottawa did not respond to a request for comment on Monday.